The Development of a Rectal Enema as Microbicide (DREAM) Program addresses the critical need to develop a highly effective, safe, and more behaviorally-congruent alternative for the prevention of rectal HIV infection. The overall goal of the program is to develop a single dose pericoital enema to deliver a tenofovir (TFV) prodrug capable of providing one week of HIV protection. This strategy (1) builds upon proven high levels of efficacy of TFV-based pre-exposure prophylaxis (PrEP) in adherent persons, (2) directly targets adherence as the greatest weakness of PrEP regimens, and (3) employs an array of innovative tools which we have refined in two prior U19 IPCP rectal microbicide programs. Given the common practice of rectal douching with an enema prior to receptive anal sex, we selected the enema as a dosing strategy requiring little behavioral change compared to oral and other topical approaches. Rectal delivery also reduces systemic exposure compared to oral and injectable approaches. We plan pharmacokinetic enhancements to (1) increase TFV bioavailability to colon tissue CD4+ cells by optimizing one of three competing TFV prodrugs with far greater tissue and cellular uptake than TFV itself - TFV disoproxil fumarate, TFV alafenamide fumarate, and CMX157 - and (2) explore sustained product release. Beyond the primary goal of producing a single PrEP enema candidate, two secondary themes are intrinsic to the success of this program as indicated in goals 2 and 3 below. The Program integrates four projects (Pre-Clinical, Tissue modeling, Clinical, IND-enabling) and three cores (Administrative, Regulatory, and Analytical) to achieve the overarching Program Goals: Goal 1: Develop a rectally-applied, HIV preventive TFV prodrug enema using a competitive pipeline process reducing multiple candidates through mouse, macaque, and pre-phase I human studies. Goal 2: Develop data-driven dosing recommendations for non-human primate to human studies (allometric scaling) based on both multi-compartment pharmacokinetics and antiretroviral pharmacodynamics. Goal 3: Build models enabling clinical trial simulation based on actual TFV target tissue (and other compartment) concentrations integrated with viral dynamic models to enhance future study design/efficiency.